Why won't iTunes allow my iPhone 5 and iPhone 6 to play 176.4/24 AIFF files created in December of 2014 and January of 2015, but will allow my iPhone 5 and iPhone 6 to play 176.4/24 AIFF files created before December of 2014?

Question

When I buy and download high resolution music files (FLAC and DSD), I convert them to AIFF files and add them to my iTunes music library.  Specifically, I have been converting DSD64 files to 176.4/24 AIFF files.  These AIFF files (modified in some respects by iTunes) have been synched to my old iPhone 5 and new iPhone 6.  Until December, every 176.4/24 AIFF file played as expected.  In December, I purchased two DSD64 albums, which I converted to 176.4/24 AIFF files using AudirvanaPlus 1.5.  These 176.4/24 AIFF files will not play on either iPhone.  When I converted those DSD64 albums to 88.2/24 AIFF files, they played on both iPhones.  In December, I also purchased several 192/24 FLAC albums and converted them to 192/24 AIFF files using Amarra HiFi.  These 192/24 AIFF files play properly on both iPhones.
Why won't iTunes allow my iPhone 5 and iPhone 6 to play 176.4/24 AIFF files created in December of 2014 and January of 2015, but will allow my iPhone 5 and iPhone 6 to play 176.4/24 AIFF files created before December of 2014?

Answer 1

I have a similar problem and have spent three sequential days at the Apple Genius Bar before we were able to exclude most other possibilities and found that certain files (in my case all mp3s from CDs I own) that play just fine in iTunes 11.0.1 and that used to play in iOS 6.0.1 do not play in iOS 6.1. We restored the phone to factory settings and synced only a few of the music files that were problematic. They still did not play. We reproduced the problem on my iPad mini (iOS6.1).
Apple Telephone Support suggestion was to convert all mp3 files in iTunes to AAC (which according to Apple Website may degrade sound quality). No further suggestions or escalation but a recommendation to place comments on www.apple.com/feedback and, if there are enough complaints, someone at Apple might take an interest in this problem. Something has changed in iOS 6.1 where files that played on prior mobile system software no longer work.
Apple, please pay attention to this glitch with iOS 6.1.